The invention relates to a process of finishing outer joint parts formed in a non-cutting way and intended for constant velocity joints in the form of tripode joints or ball joints; the outer joint parts have a longitudinal axis and an inner recess which extends in the direction of the longitudinal axis and which is substantially undercut-free. The inner recess is provided with tracks for form-fittingly receiving rolling members which, in turn, are held in a form-fitting connection by the inner joint part. The tracks comprise hardened contact zones for the rolling contact of rolling members. Furthermore, the invention relates to a device for finishing outerjoint parts formed in a non-cutting way and intended for constant velocity joints of the above-mentioned type.
The invention relates to tripode joints and ball joints in the form of UF joints (undercut-free) and DO joints (double offset). For reasons of cost, the process of forming such joints in a non-cutting way is nowadays perfected to such an extent that the tracks with their respective roller contact zones (in the case of tripode joints) and ball contact zones (in the case of ball joints) comprise their finish dimension and do not require subsequent machining. It is, however, necessary to harden at least the contact zones on which the rolling members run, with such hardening usually being carried out in the form of induction hardening. In view of the axially asymmetric , conditions of mass and thermal capacity at the respective ends of the tracks, i.e. due to a relative heat accumulation at the axial ends of the contact zones to be hardened, the contact zones are subject to hardness distortions which cannot be perfectly compensated for, not even by an axially adapted introduction of heat and/or cooling during the hardening operation. In consequence, the contact zones, along their axial length, are radially distorted at their ends, and the internal dimension of the inner recess between symmetrically opposed contact zones at the axial ends of the outer joint part is normally reduced. Subsequent machining in the form of grinding is impossible for reasons of costs. As a result the joint suffers from tolerance defects with too close a fit at the open end of the outer joint part and/or too wide a fit in the rear inner region of the outer joint part.
It is therefore the object of the present invention to provide a process of and device for finishing outer joint parts of said type, which improve the dimensional accuracy of the hardened contact zones of the tracks and thus reduce the tolerance defects at the joint.
The objective is achieved by providing a process which is characterised by the following sequence of process stages:
non-cutting forming of the outer joint part, surface-layer-hardening of the inner recess at least along the length of the contact zones, for the purpose of producing a hardened surface layer, at least in the region of the contact zones, above an unhardened matrix and
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
By leaving a non-calibrated surface strip between each two surface-layer-hardened, calibrated contact zones, it is possible to sufficiently deform the hardened contact zones with the matrix or within the matrix without there occurring any fractures of the hardened contact zones. It is particularly advantageous if, while calibrating the contact zones, the unhardened matrix behind the hardened surface layer is made to flow over large portions, starting from the outer surface of the component; circumferential movements in the matrix should also be permitted. Flowing in the matrix, which occurs by generating an inwardly directed pressure on the outer surface of the component should take place in those cases where the internal dimension of the inner recess between opposed contact zones has to be reduced and also in those cases where said internal dimension has to be increased. The hardened surface layer can be produced with a thickness of up 1.2 mm. The stresses necessarily occurring within the hardened calibrated strips of the surface layer can be reduced by a subsequent heat treatment without incurring a substantial loss of hardness. If the radial dimension of the inner recess between opposed hardened contact zones is too small after hardening, especially at the axial end of the outer joint part, it can be increased by pressing in strips of (hardened) surface layers into the matrix. If, on the other hand, the radial dimension of the inner recess between opposed hardened contact zones is too large after hardening, it can be reduced by pressing in the matrix material behind the strip of the (hardened) surface layers. Both measures are effected by axially pressing a calibrating mandrel into the outer joint part in a first process stage and by radially pressing outer calibrating jaws on to the outer joint part in a second process stage while the calibrating mandrel is in an introduced condition. Both measures can be carried out jointly in one calibrating operation in different regions of the contact zones.
According to a first variant in accordance with the invention, there is proposed a process having the following process stages:
non-cutting forming of the outer joint part,
surface-layer-hardening of the inner recess along the length of the contact zones while
producing a hardened surface layer in the region of the contact zones above an unhardened matrix, and retaining an unhardened surface strip between the adjoining contact zones,
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
Between each two surface-layer-hardened contact zones there is retained a surface strip in which the unhardened matrix forms the inner face of the inner recess. This permits high deformation rates, and the internal dimension of the inner recess between two symmetrically opposed contact zones can be changed by up to 0.3 mm.
If the inventive method is applied to the outer parts of tripode joints which comprise three inner longitudinally extending roller tracks which each comprise pairs of symmetrically arranged roller contact zones, it is proposed that between the roller contact zones of one roller track, there is retained an unhardened strip of the matrix and, according to a preferred embodiment, that between adjoining roller contact zones of two adjoining roller tracks, there is retained an unhardened strip of the matrix. If the inventive method is applied to the outer parts of ball joints which comprise at least three longitudinally extending ball grooves which form pairs of symmetrically arranged ball contact zones, it is proposed that between adjoining ball contact zones of two adjoining ball grooves, there is retained an unhardened strip of the matrix. In such a case, either the surface layer of an entire ball groove is completely hardened or it can be proposed that between the two ball contact zones of a ball groove, there is also retained an unhardened strip of the matrix. In both cases, the two ball contact zones of a ball groove can be deformed relative to one another.
According to a second variant in accordance with the invention, there is proposed a process having the following process stages:
non-cutting forming of the outer joint part,
surface-layer-hardening of the inner recess along the length of the contact zones, thereby producing a hardened surface layer which is continuously hardened in the inner recess, above an unhardened matrix,
calibrating the contact zones in respect of their radial positions and axial linearity by displacing the hardened surface layer in the region of the contact zones within the unhardened matrix.
In this case, the inner surface of the inner recess is surface-layer-hardened all around in a simplified way. As a result, when calibrating the contact zones, the intermediate surface-layer-hardened regions are subject to stresses which must not lead to an uncontrolled formation of cracks. The deformation rates in this case are slightly limited, and the internal dimension of the inner recess between two symmetrically opposed contact zones can be changed by up to 0.2 mm. Any stresses can be reduced after the calibration process by heat treatment.
If the inventive method is used for the outer joint parts of tripode joints which comprise three longitudinally extending roller tracks which each comprise pairs of symmetrically arranged roller contact zones, it is proposed that between the calibrated roller contact zones of a roller track, there are retained non-calibrated strips each, and in a further preferred embodiment it is proposed that between adjoining calibrated roller contact zones of adjoining roller tracks, there are retained non-calibrated strips each. This is achieved in that, in these areas, the component wall is not subjected to any process operations, neither from the inside nor from the outside. It the inventive method is applied to the outer parts of ball joints which comprise at least three longitudinally extending ball grooves which each form pairs of symmetrically arranged ball contact zones, it is proposed that between the two ball contact zones of a ball groove, there are retained largely non-calibrated strips each. In addition, it is proposed that between adjoining calibrated ball contact zones of two adjoining ball grooves, there are retained largely non-calibrated strips each. This is achieved in that, in these areas, the component wall is not subjected to any joint process operations, neither from the inside nor from the outside. In any case, the two ball contact zones of a ball groove can be deformed relative to one another.
According to a preferred embodiment it is proposed that calibration takes place by pressure-agent-operated tools and that the calibration process is controlled by regulating and limiting the pressure of the pressure agent. As a result, any scatter as regards the starting dimension of the workpiece, especially also at the outer circumference of the outer joint part, is of no significance.
A device for carrying out the above-explained method is characterised by
a rigid calibrating mandrelxe2x80x94especially with a straight, non-round cylindrical memberxe2x80x94which can be axially introduced into the outer joint part, and by
a number of calibrating jaws which at least corresponds to the number of tracksxe2x80x94especially with straight, non-round cylindrical facesxe2x80x94which can be radially moved to the calibrating mandrel and whose radial dividing planes are positioned symmetrically between two hardened contact zones to be calibrated.
As a result, the calibrating mandrel and the calibrating jaws, in the region of their effective faces, comprise parallel mantle lines whose purpose it is to co-operate by producing correspondingly parallel mantle lines on the contact faces. At its end which has to be introduced first into the outer joint part, the calibrating mandrel can be provided with large introducing radii.
According to a further preferred embodiment, it has to be ensured that in the case of tripode joints, there have to be provided six calibrating jaws, which number corresponds to the number of hardened contact zones. In the case of ball joints, a number of calibrating jaws corresponding to the number of ball grooves can be sufficient. As already indicated above, the calibrating mandrel is first introduced into an axially held outer joint part; this can take place with play, or parts of the hardened contact zones can already be radially displaced while being introduced, and straightened under plastic deformation of the matrix. During the subsequent process stage, the calibrating jaws are radially fed in and in the process, the outer joint part is deformed in such a way that plastic deformation of the matrix behind the hardened tracks takes place to such extent that the hardened contact zones rest against the calibrating mandrel with approximately an equal amount of pre-pressure.
In order to permit a sufficient degree of plastic deformation of the matrix, the calibrating mandrel is provided with supporting zones for the hardened roller contact zones or ball contact zones and forms intermediate clearance cuts which, up to the completion of the calibrating operation, remain contact-free relative to the inner surface of the outer joint part. For the same purpose it is proposed that the calibrating jaws comprise longitudinally extending pressure ribs and intermediate clearance cuts into which material can flow during plastic deformations but contact between the outer face of the outer joint part and the regions of the clearance cut is permitted. In any case, displaced material can enter the region of the dividing planes between two calibrating jaws. Even at the end of the calibrating operation, two calibrating jaws remain at a circumferential distance between the dividing planes.
The calibrating jaws are preferably received in a supporting ring in which they are radially displaceable, and the radial displacement can be achieved by fixed wedges and sliding wedges co-operating with one another. The calibrating jaws and an inserted outer joint part are placed on to a supporting plate of a counter punch, the calibrating mandrel connected to an upper punch is introduced and one punch face at the calibrating mandrel is lowered on to the sliding wedges. The pressurised counter punch is able to give way, together with the calibrating jaws and the outer joint part, so that a sliding movement can take place only between the sliding wedges and the fixed wedges, whereas the sliding wedges can move relative to the calibrating jaws and the outer joint part in the radial direction only. When a predetermined pressure differential is achieved between the punch and counter punch, the calibrating process is completed.
According to a further preferred embodiment, holding-down devices displaceable in guiding means are arranged on the upper face of the supporting ring.. After the calibrating process has been completed, the holding-down devices are moved across the end face of the outer joint part and the calibrating mandrel is withdrawn.